As a corollary to that thought, the non-citizen has to regularly re-apply to remain in the US. I have a non-citizen friend who is married to a US citizen, and he has to do regular interviews with US immigrations officers to renew his green card and maintain his ability to work in the US. It's possible, though unlikely, that he could have either or both permissions denied by some bureaucrat.

There's something wrong about that. My wife is a "green card" resident alien. Although her original green card said "PERMANENT" in bold letters across the top, it expired one (two?) years after issuance. Once that was renewed, however, "permanent" means "permanent." No renewals, no interviews. And she is allowed to work.